The number of polio cases worldwide reached a record low in 2012, giving experts confidence that the disease can finally be eradicated, according to presentations made at a major US conference.

Just 177 cases were recorded globally through October 2012, down from 502 during the same period last year, said virologists attending the annual meeting of the American Society of Tropical Medicine and Hygiene in Atlanta.

But the experts said challenges in the fight against polio remain, citing a doubling this year of the number of cases in Nigeria, and persistent difficulties in Pakistan.

Pakistan, Nigeria and Afghanistan are the only countries where polio remains endemic. Experts are trying to eliminate polio from those places, making it only the second disease after smallpox to be completely eradicated.

Steven Wassilak, a polio expert at the US Centers for Disease Control and Prevention, said new data from Pakistan shows that one of the two types of wild polio virus prevalent in the South Asian country is close to being wiped out.

“There have not been any Type 3 cases reported for six months, which is the longest gap in incidence there to date,” Wassilak said, according to a press release.

But Anita Zaidi, a pediatrician at Aga Khan University in the Pakistani city of Karachi, said wary parents are still refusing to allow their children to take part in vaccination drives -- a problem that is not easily solved.

“That is a big challenge and not something that can be overcome only by expanding immunisation campaigns,” Zaidi said, while noting the progress made in bringing vaccinations to rural communities.

Zaidi said Karachi was the only large city in the world that had failed to stamp out polio transmission, and condemned the killing of a health worker in the city involved in a vaccination drive.

Wassilak voiced hope that the problem of parental reluctance -- which also exists in Nigeria -- could be overcome, citing India as an example. That country has not reported a polio infection since January 2011.

“It requires working more closely with community leaders and greater political commitment at all levels, which is what we are seeing in both Pakistan and Nigeria,” he said.

Experts are worried about polio cases in Nigeria, as in the past, infections have spread to Sudan, Chad and 23 other countries.

The highly infectious disease affects mainly those under the age of five and can cause paralysis in a matter of hours. Some cases can be fatal.